using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;

public static class StringExtensions
{
	/// <summary>
	/// 将string转换为DateTime，若转换失败，则返回默认值。  
	/// </summary>
	/// <returns></returns>
	public static DateTime? ToDateTime(this string str, DateTime? defaultValue = null)
	{
		DateTime val;
		if (string.IsNullOrWhiteSpace(str))
		{
			return defaultValue.GetValueOrDefault();
		}
		if (str.Contains("-") || str.Contains("/"))
		{
			if (DateTime.TryParse(str, out val))
				return val;

			return defaultValue.GetValueOrDefault();
		}
		else
		{
			int length = str.Length;
			switch (length)
			{
				case 4:
					if (DateTime.TryParseExact(str, "yyyy", CultureInfo.CurrentCulture, DateTimeStyles.None, out val))
						return val;
					return defaultValue.GetValueOrDefault();
				case 6:
					if (DateTime.TryParseExact(str, "yyyyMM", CultureInfo.CurrentCulture, DateTimeStyles.None, out  val))
						return val;
					return defaultValue.GetValueOrDefault();
				case 8:
					if (DateTime.TryParseExact(str, "yyyyMMdd", CultureInfo.CurrentCulture, DateTimeStyles.None, out  val))
						return val;
					return defaultValue.GetValueOrDefault();
				case 10:
					if (DateTime.TryParseExact(str, "yyyyMMddHH", CultureInfo.CurrentCulture, DateTimeStyles.None, out  val))
						return val;
					return defaultValue.GetValueOrDefault();
				case 12:
					if (DateTime.TryParseExact(str, "yyyyMMddHHmm", CultureInfo.CurrentCulture, DateTimeStyles.None, out  val))
						return val;
					return defaultValue.GetValueOrDefault();
				case 14:
					if (DateTime.TryParseExact(str, "yyyyMMddHHmmss", CultureInfo.CurrentCulture, DateTimeStyles.None, out  val))
						return val;
					return defaultValue.GetValueOrDefault();
				default:
					if (DateTime.TryParseExact(str, "yyyyMMddHHmmss", CultureInfo.CurrentCulture, DateTimeStyles.None, out  val))
						return val;
					return defaultValue.GetValueOrDefault();
			}
		}
	}
	/// <summary>
	/// 强制转换类型
	/// </summary>
	/// <typeparam name="TResult"></typeparam>
	/// <param name="source"></param>
	/// <returns></returns>
	public static IEnumerable<TResult> CastSuper<TResult>(this IEnumerable source)
	{
		foreach (object item in source)
		{
			yield return (TResult)Convert.ChangeType(item, typeof(TResult));
		}
	}

	// 转换为long
	public static long ToLong(this string str, long defaultValue = 0L) =>
		long.TryParse(str, out var result) ? result : defaultValue;

	// 转换为int
	public static int ToInt(this string str, int defaultValue = 0) =>
		int.TryParse(str, out var result) ? result : defaultValue;

	// 转换为short
	public static short ToShort(this string str, short defaultValue = 0) =>
		short.TryParse(str, out var result) ? result : defaultValue;

	// 转换为decimal
	public static decimal ToDecimal(this string str, decimal defaultValue = 0m) =>
		decimal.TryParse(str, NumberStyles.Any, CultureInfo.InvariantCulture, out var result) ? result : defaultValue;

	// 转换为bool
	public static bool ToBool(this string str, bool defaultValue = false) =>
		bool.TryParse(str, out var result) ? result : defaultValue;

	// 转换为float
	public static float ToFloat(this string str, float defaultValue = 0f) =>
		float.TryParse(str, NumberStyles.Any, CultureInfo.InvariantCulture, out var result) ? result : defaultValue;

	// 转换为double
	public static double ToDouble(this string str, double defaultValue = 0d) =>
		double.TryParse(str, NumberStyles.Any, CultureInfo.InvariantCulture, out var result) ? result : defaultValue;

	// 转换为Guid
	public static Guid ToGuid(this string str, Guid defaultValue = default) =>
		Guid.TryParse(str, out var guid) ? guid : defaultValue;

}